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2 <html><head><title>A Few Coding Standards</title></head>
5 <table width="100%" bgcolor="#330077" border=0 cellpadding=4 cellspacing=0>
6 <tr><td> <font size=+5 color="#EEEEFF" face="Georgia,Palatino,Times,Roman"><b>A Few Coding Standards</b></font></td>
10 <li><a href="#introduction">Introduction</a>
11 <li><a href="#mechanicalissues">Mechanical Source Issues</a>
13 <li><a href="#sourceformating">Source Code Formatting</a>
15 <li><a href="#scf_commenting">Commenting</a>
16 <li><a href="#scf_commentformat">Comment Formatting</a>
17 <li><a href="#scf_codewidth">Source Code Width</a>
18 <li><a href="#scf_spacestabs">Use Spaces Instead of Tabs</a>
19 <li><a href="#scf_indentation">Indent Code Consistently</a>
21 <li><a href="#compilerissues">Compiler Issues</a>
23 <li><a href="#ci_warningerrors">Treat Compiler Warnings Like Errors</a>
24 <li><a href="#ci_cpp_features">Which C++ features can I use?</a>
25 <li><a href="#ci_portable_code">Write Portable Code</a>
28 <li><a href="#styleissues">Style Issues</a>
30 <li><a href="#macro">The High Level Issues</a>
32 <li><a href="#hl_module">A Public Header File <b>is</b> a Module</a>
33 <li><a href="#hl_dontinclude">#include as Little as Possible</a>
34 <li><a href="#hl_privateheaders">Keep "internal" Headers Private</a>
36 <li><a href="#micro">The Low Level Issues</a>
38 <li><a href="#hl_assert">Assert Liberally</a>
39 <li><a href="#hl_preincrement">Prefer Preincrement</a>
40 <li><a href="#hl_exploitcpp">Exploit C++ to its Fullest</a>
42 <li><a href="#iterators">Writing Iterators</a>
44 <li><a href="#seealso">See Also</a>
48 <!-- *********************************************************************** -->
49 </ul><table width="100%" bgcolor="#330077" border=0 cellpadding=4 cellspacing=0><tr><td align=center><font color="#EEEEFF" size=+2 face="Georgia,Palatino"><b>
50 <a name="introduction">Introduction
51 </b></font></td></tr></table><ul>
52 <!-- *********************************************************************** -->
54 This document attempts to describe a few coding standards that are being used in the LLVM source tree. Although no coding standards should be regarded as absolute requirements to be followed in all instances, coding standards can be useful.<p>
56 This document intentionally does not prescribe fixed standards for religious issues such as brace placement and space usage. For issues like this, follow the golden rule:
59 <blockquote><b>If you are adding a significant body of source to a project, feel free to use whatever style you are most comfortable with. If you are extending, enhancing, or bug fixing already implemented code, use the style that is already being used so that the source is uniform and easy to follow.</b></blockquote>
61 The ultimate goal of these guidelines is the increase readability and maintainability of our common source base. If you have suggestions for topics to be included, please mail them to <a href="mailto:sabre@nondot.org">Chris</a>.<p>
64 <!-- *********************************************************************** -->
65 </ul><table width="100%" bgcolor="#330077" border=0 cellpadding=4 cellspacing=0><tr><td align=center><font color="#EEEEFF" size=+2 face="Georgia,Palatino"><b>
66 <a name="mechanicalissues">Mechanical Source Issues
67 </b></font></td></tr></table><ul>
68 <!-- *********************************************************************** -->
70 <!-- ======================================================================= -->
71 </ul><table width="100%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0><tr><td> </td><td width="100%"> <font color="#EEEEFF" face="Georgia,Palatino"><b>
72 <a name="sourceformating">Source Code Formatting
73 </b></font></td></tr></table><ul>
76 <!-- _______________________________________________________________________ -->
77 </ul><a name="scf_commenting"><h4><hr size=0>Commenting</h4><ul>
79 Comments are one critical part of readability and maintainability. Everyone knows they should comment, so should you. :) Although we all should probably comment our code more than we do, there are a few very critical places that documentation is very useful:<p>
82 <h4><li>File Headers</h4>
83 Every source file should have a header on it that describes the basic purpose of the file. If a file does not have a header, it should not be checked into CVS. Most source trees will probably have a standard file header format. The standard format for the LLVM source tree looks like this:<p>
86 //===-- llvm/Instruction.h - Instruction class definition --------*- C++ -*--=//
88 // This file contains the declaration of the Instruction class, which is the
89 // base class for all of the VM instructions.
91 //===----------------------------------------------------------------------===//
94 A few things to note about this particular format. The "<tt>-*- C++ -*-</tt>" string on the first line is there to tell Emacs that the source file is a C++ file, not a C file (Emacs assumes .h files are C files by default [Note that tag this is not neccesary in .cpp files]). The name of the file is also on the first line, along with a very short description of the purpose of the file. This is important when printing out code and flipping though lots of pages.<p>
96 The main body of the description does not have to be very long in most cases. Here it's only two lines. If an algorithm is being implemented or something tricky is going on, a reference to the paper where it is published should be included, as well as any notes or "gotchas" in the code to watch out for.<p>
99 <h4><li>Class overviews</h4>
101 Classes are one fundemental part of a good object oriented design. As such, a class definition should have a comment block that explains what the class is used for... if it's not obvious. If it's so completely obvious your grandma could figure it out, it's probably safe to leave it out. Naming classes something sane goes a long ways towards avoiding writing documentation. :)<p>
104 <h4><li>Method information</h4>
106 Methods defined in a class (as well as any global functions) should also be documented properly. A quick note about what it does any a description of the borderline behaviour is all that is neccesary here (unless something particularly tricky or insideous is going on). The hope is that people can figure out how to use your interfaces without reading the code itself... that is the goal metric.<p>
108 Good things to talk about here are what happens when something unexpected happens: does the method return null? Abort? Format your hard disk?<p>
112 <!-- _______________________________________________________________________ -->
113 </ul><a name="scf_commentformat"><h4><hr size=0>Comment Formatting</h4><ul>
115 In general, prefer C++ style (<tt>//</tt>) comments. They take less space, require less typing, don't have nesting problems, etc. There are a few cases when it is useful to use C style (<tt>/* */</tt>) comments however:<p>
118 <li>When writing a C code: Obviously if you are writing C code, use C style comments. :)
119 <li>When writing a header file that may be #included by a C source file.
120 <li>When writing a source file that is used by a tool that only accepts C style comments.
123 To comment out a large block of code, use <tt>#if 0</tt> and <tt>#endif</tt>. These nest properly and are better behaved in general than C style comments.<p>
126 <!-- _______________________________________________________________________ -->
127 </ul><a name="scf_codewidth"><h4><hr size=0>Source Code Width</h4><ul>
129 Write your code to fit within 80 columns of text. This helps those of us who like to print out code and look at your code in an xterm without resizing it.
132 <!-- _______________________________________________________________________ -->
133 </ul><a name="scf_spacestabs"><h4><hr size=0>Use Spaces Instead of Tabs</h4><ul>
135 In all cases, prefer spaces to tabs in source files. People have different prefered indentation levels, and different styles of indentation that they like... this is fine. What isn't is that different editors/viewers expand tabs out to different tab stops. This can cause your code to look completely unreadable, and it is not worth dealing with.<p>
137 As always, follow the <a href="#goldenrule">Golden Rule</a> above: follow the style of existing code if your are modifying and extending it. If you like four spaces of indentation, <b>DO NOT</b> do that in the middle of a chunk of code with two spaces of indentation. Also, do not reindent a whole source file: it make for incredible diffs that are absolutely worthless.<p>
140 <!-- _______________________________________________________________________ -->
141 </ul><a name="scf_indentation"><h4><hr size=0>Indent Code Consistently</h4><ul>
143 Okay, your first year of programming you were told that indentation is important. If you didn't believe and internalize this then, now is the time. Just do it.<p>
148 <!-- ======================================================================= -->
149 </ul><table width="100%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0><tr><td> </td><td width="100%"> <font color="#EEEEFF" face="Georgia,Palatino"><b>
150 <a name="compilerissues">Compiler Issues
151 </b></font></td></tr></table><ul>
154 <!-- _______________________________________________________________________ -->
155 </ul><a name="ci_warningerrors"><h4><hr size=0>Treat Compiler Warnings Like Errors</h4><ul>
157 If your code has compiler warnings in it, something is wrong: you aren't casting values correctly, your have "questionable" constructs in your code, or you are doing something legitimately wrong. Compiler warnings can cover up legitimate errors in output and make dealing with a translation unit difficult.<p>
159 It is not possible to prevent all warnings from all compilers, nor is it desirable. Instead, pick a standard compiler (like <tt>gcc</tt>) that provides a good thorough set of warnings, and stick to them. At least in the case of <tt>gcc</tt>, it is possible to work around any spurious errors by changing the syntax of the code slightly. For example, an warning that annoys me occurs when I write code like this:<p>
162 if (V = getValue()) {
167 <tt>gcc</tt> will warn me that I probably want to use the <tt>==</tt> operator, and that I probably mistyped it. In most cases, I haven't, and I really don't want the spurious errors. To fix this particular problem, I rewrite the code like this:<p>
170 if ((V = getValue())) {
175 ...which shuts <tt>gcc</tt> up. Any <tt>gcc</tt> warning that annoys you can be fixed by massaging the code appropriately.<p>
177 These are the <tt>gcc</tt> warnings that I prefer to enable: <tt>-Wall -Winline -W -Wwrite-strings -Wno-unused</tt><p>
180 <!-- _______________________________________________________________________ -->
181 </ul><a name="ci_cpp_features"><h4><hr size=0>Which C++ features can I use?</h4><ul>
183 Compilers are finally catching up to the C++ standard. Most compilers implement most features, so you can use just about any features that you would like. In the LLVM source tree, I have chosen to not use these features:<p>
186 <li>Exceptions: Exceptions are very useful for error reporting and handling exceptional conditions. I do not use them in LLVM because they do have an associated performance impact (by restricting restructuring of code), and parts of LLVM are designed for performance critical purposes.<p>
188 Just like most of the rules in this document, this isn't a hard and fast requirement. Exceptions are used in the Parser, because it simplifies error reporting <b>significantly</b>, and the LLVM parser is not at all in the critical path.<p>
190 <li>RTTI: RTTI has a large cost in terms of executable size, and compilers are not yet very good at stomping out "dead" class information blocks. Because of this, typeinfo and dynamic cast are not used.
193 Other features, such as templates (without partial specialization) can be used freely. The general goal is to have clear, consise, performant code... if a technique assists with that then use it.<p>
196 <!-- _______________________________________________________________________ -->
197 </ul><a name="ci_portable_code"><h4><hr size=0>Write Portable Code</h4><ul>
199 In almost all cases, it is possible and within reason to write completely portable code. If there are cases where it isn't possible to write portable code, isolate it behind a well defined (and well documented) interface.<p>
201 In practice, this means that you shouldn't assume much about the host compiler, including its support for "high tech" features like partial specialization of templates. In fact, Visual C++ 6 could be an important target for our work in the future, and we don't want to have to rewrite all of our code to support it.<p>
205 <!-- *********************************************************************** -->
206 </ul><table width="100%" bgcolor="#330077" border=0 cellpadding=4 cellspacing=0><tr><td align=center><font color="#EEEEFF" size=+2 face="Georgia,Palatino"><b>
207 <a name="styleissues">Style Issues
208 </b></font></td></tr></table><ul>
209 <!-- *********************************************************************** -->
212 <!-- ======================================================================= -->
213 </ul><table width="100%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0><tr><td> </td><td width="100%"> <font color="#EEEEFF" face="Georgia,Palatino"><b>
214 <a name="macro">The High Level Issues
215 </b></font></td></tr></table><ul>
218 <!-- _______________________________________________________________________ -->
219 </ul><a name="hl_module"><h4><hr size=0>A Public Header File <b>is</b> a Module</h4><ul>
221 C++ doesn't do too well in the modularity department. There is no real encapsulation or data hiding (unless you use expensive protocol classes), but it is what we have to work with. When you write a public header file (in the LLVM source tree, they live in the top level "include" directory), you are defining a module of functionality.<p>
223 Modules should be completely independent of each other, except for their dependence. A module is not just a class, a function, or a namespace: <a href="http://www.cuj.com/articles/2000/0002/0002c/0002c.htm">it's a collection of these</a> that defines an interface. This interface may be several functions, classes or data structures, but the important issue is how they work together.<p>
225 <!--One example of this is the <tt>llvm/include/llvm/CFG.h</tt> file. It defines a collection of global functions, template classes, and member functions that are syntactically unrelated to each other. Semantically, however, they all provide useful functionality for operating on a CFG, and so they are bound together.<p> -->
227 In general, a module should be implemented with one or more <tt>.cpp</tt> files. Each of these <tt>.cpp</tt> files should include the header that defines their interface first. This ensure that all of the dependences of the module header have been properly added to the module header itself, and are not implicit. System headers should be included after user headers for a translation unit.<p>
230 <!-- _______________________________________________________________________ -->
231 </ul><a name="hl_dontinclude"><h4><hr size=0>#include as Little as Possible</h4><ul>
233 <tt>#include</tt> hurts compile time performance. Don't do it unless you have to, especially in header files.<p>
235 But wait, sometimes you need to have the definition of a class to use it, or to inherit from it. In these cases go ahead and #include that header file. Be aware however that there are many cases where you don't need to have the full definition of a class. If you are using a pointer or reference to a class, you don't need the header file. If you are simply returning a class instance from a prototyped function or method, you don't need it. In fact, for most cases, you simply don't need the definition of a class... and not <tt>#include</tt>'ing speeds up compilation.<p>
237 It is easy to try to go too overboard on this recommendation, however. You <b>must</b> include all of the header files that you are using, either directly or indirectly (through another header file). To make sure that you don't accidently forget to include a header file in your module header, make sure to include your module header <b>first</b> in the implementation file (as mentioned above). This way there won't be any hidden dependencies that you'll find out about later...<p>
240 <!-- _______________________________________________________________________ -->
241 </ul><a name="hl_privateheaders"><h4><hr size=0>Keep "internal" Headers Private</h4><ul>
243 Many modules have a complex implementation that causes them to use more than one implementation (<tt>.cpp</tt>) file. It is often tempting to put the internal communication interface (helper classes, extra functions, etc) in the public module header file. Don't do this. :)<p>
245 If you really need to do something like this, put a private header file in the same directory as the source files, and include it locally. This ensures that your private interface remains private and undisturbed by outsiders.<p>
247 Note however, that it's okay to put extra implementation methods a public class itself... just make them private (or protected), and all is well.<p>
250 <!-- ======================================================================= -->
251 </ul><table width="100%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0><tr><td> </td><td width="100%"> <font color="#EEEEFF" face="Georgia,Palatino"><b>
252 <a name="micro">The Low Level Issues
253 </b></font></td></tr></table><ul>
256 <!-- _______________________________________________________________________ -->
257 </ul><a name="hl_assert"><h4><hr size=0>Assert Liberally</h4><ul>
259 Use the "<tt>assert</tt>" function to its fullest. Check all of your preconditions and assumptions, you never know when a bug (not neccesarily even yours) might be caught early by an assertion, which reduces debugging time dramatically. The "<tt>assert.h</tt>" header file is probably already included by the header files you are using, so it doesn't cost anything to use it.<p>
261 To further assist with debugging, make sure to put some kind of error message in the assertion statement (which is printed if the assertion is tripped). This helps the poor debugging make sense of why an assertion is being made and enforced, and hopefully what to do about it. Here is one complete example:<p>
264 inline Value *getOperand(unsigned i) {
265 assert(i < Operands.size() && "getOperand() out of range!");
270 Here are some examples:
273 assert(Ty->isPointerType() && "Can't allocate a non pointer type!");
275 assert((Opcode == Shl || Opcode == Shr) && "ShiftInst Opcode invalid!");
277 assert(idx < getNumSuccessors() && "Successor # out of range!");
279 assert(V1.getType() == V2.getType() && "Constant types must be identical!");
281 assert(isa<PHINode>(Succ->front()) && "Only works on PHId BBs!");
284 You get the idea...<p>
287 <!-- _______________________________________________________________________ -->
288 </ul><a name="hl_preincrement"><h4><hr size=0>Prefer Preincrement</h4><ul>
290 Hard fast rule: Preincrement (++X) may be no slower than postincrement (X++) and could very well be a lot faster than it. Use preincrementation whenever possible.<p>
292 The semantics of postincrement include making a copy of the value being incremented, returning it, and then preincrementing the "work value". For primitive types, this isn't a big deal... but for iterators, it can be a huge issue (for example, some iterators contains stack and set objects in them... copying an iterator could invoke the copy ctor's of these as well). In general, get in the habit of always using preincrement, and you won't have a problem.<p>
295 <!-- _______________________________________________________________________ -->
296 </ul><a name="hl_exploitcpp"><h4><hr size=0>Exploit C++ to its Fullest</h4><ul>
298 C++ is a powerful language. With a firm grasp on its capabilities, you can make write effective, consise, readable and maintainable code all at the same time. By staying consistent, you reduce the amount of special cases that need to be remembered. Reducing the total number of lines of code you write is a good way to avoid documentation, and avoid giving bugs a place to hide.<p>
300 For these reasons, come to know and love the contents of your local <algorithm> header file. Know about <functional> and what it can do for you. C++ is just a tool that wants you to master it. :)<p>
304 <!-- ======================================================================= -->
305 </ul><table width="100%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0><tr><td> </td><td width="100%"> <font color="#EEEEFF" face="Georgia,Palatino"><b>
306 <a name="iterators">Writing Iterators
307 </b></font></td></tr></table><ul>
309 Here's a pretty good summary of how to write your own data structure iterators in a way that is compatible with the STL, and with a lot of other code out there (slightly edited by Chris):<p>
312 From: Ross Smith <ross.s@ihug.co.nz>
313 Newsgroups: comp.lang.c++.moderated
314 Subject: Writing iterators (was: Re: Non-template functions that take iterators)
315 Date: 28 Jun 2001 12:07:10 -0400
318 > Any pointers handy on "writing STL-compatible iterators for
321 I'll give it a try...
323 The usual situation requiring user-defined iterators is that you have
324 a type that bears some resemblance to an STL container, and you want
325 to provide iterators so it can be used with STL algorithms. You need
326 to ask three questions:
328 First, is this simply a wrapper for an underlying collection of
329 objects that's held somewhere as a real STL container, or is it a
330 "virtual container" for which iteration is (under the hood) more
331 complicated than simply incrementing some underlying iterator (or
332 pointer or index or whatever)? In the former case you can frequently
333 get away with making your container's iterators simply typedefs for
334 those of the underlying container; your begin() function would call
335 member_container.begin(), and so on.
337 Second, do you only need read-only iterators, or do you need separate
338 read-only (const) and read-write (non-const) iterators?
340 Third, which kind of iterator (input, output, forward, bidirectional,
341 or random access) is appropriate? If you're familiar with the
342 properties of the iterator types (if not, visit
343 <a href="http://www.sgi.com/tech/stl/">http://www.sgi.com/tech/stl/</a>), the appropriate choice should be
344 obvious from the semantics of the container.
346 I'll start with forward iterators, as the simplest case that's likely
347 to come up in normal code. Input and output iterators have some odd
348 properties and rarely need to be implemented in user code; I'll leave
349 them out of discussion. Bidirectional and random access iterators are
352 The exact behaviour of a forward iterator is spelled out in the
353 Standard in terms of a set of expressions with specified behaviour,
354 rather than a set of member functions, which leaves some leeway in how
355 you actually implement it. Typically it looks something like this
356 (I'll start with the const-iterator-only situation):
362 typedef something_or_other value_type;
363 class const_iterator:
364 public std::iterator<std::forward_iterator_tag, value_type> {
365 friend class container;
367 const value_type& operator*() const;
368 const value_type* operator->() const;
369 const_iterator& operator++();
370 const_iterator operator++(int);
371 friend bool operator==(const_iterator lhs,
373 friend bool operator!=(const_iterator lhs,
381 An iterator should always be derived from an instantiation of the
382 std::iterator template. The iterator's life cycle functions
383 (constructors, destructor, and assignment operator) aren't declared
384 here; in most cases the compiler-generated ones are sufficient. The
385 container needs to be a friend of the iterator so that the container's
386 begin() and end() functions can fill in the iterator's private members
387 with the appropriate values.
389 <i>[Chris's Note: I prefer to not make my iterators friends. Instead, two
390 ctor's are provided for the iterator class: one to start at the end of the
391 container, and one at the beginning. Typically this is done by providing
392 two constructors with different signatures.]</i>
394 There are normally only three member functions that need nontrivial
395 implementations; the rest are just boilerplate.
397 const container::value_type&
398 container::const_iterator::operator*() const {
399 // find the element and return a reference to it
402 const container::value_type*
403 container::const_iterator::operator->() const {
407 If there's an underlying real container, operator*() can just return a
408 reference to the appropriate element. If there's no actual container
409 and the elements need to be generated on the fly -- what I think of as
410 a "virtual container" -- things get a bit more complicated; you'll
411 probably need to give the iterator a value_type member object, and
412 fill it in when you need to. This might be done as part of the
413 increment operator (below), or if the operation is nontrivial, you
414 might choose the "lazy" approach and only generate the actual value
415 when one of the dereferencing operators is called.
417 The operator->() function is just boilerplate around a call to
420 container::const_iterator&
421 container::const_iterator::operator++() {
422 // the incrementing logic goes here
426 container::const_iterator
427 container::const_iterator::operator++(int) {
428 const_iterator old(*this);
433 Again, the incrementing logic will usually be trivial if there's a
434 real container involved, more complicated if you're working with a
435 virtual container. In particular, watch out for what happens when you
436 increment past the last valid item -- this needs to produce an
437 iterator that will compare equal to container.end(), and making this
438 work is often nontrivial for virtual containers.
440 The post-increment function is just boilerplate again (and
441 incidentally makes it obvious why all the experts recommend using
442 pre-increment wherever possible).
444 bool operator==(container::const_iterator lhs,
445 container::const_iterator rhs) {
446 // equality comparison goes here
449 bool operator!=(container::const_iterator lhs,
450 container::const_iterator rhs) {
451 return !(lhs == rhs);
454 For a real container, the equality comparison will usually just
455 compare the underlying iterators (or pointers or indices or whatever).
456 The semantics of comparisons for virtual container iterators are often
457 tricky. Remember that iterator comparison only needs to be defined for
458 iterators into the same container, so you can often simplify things by
459 taking for granted that lhs and rhs both point into the same container
460 object. Again, the second function is just boilerplate.
462 It's a matter of taste whether iterator arguments are passed by value
463 or reference; I've shown tham passed by value to reduce clutter, but
464 if the iterator contains several data members, passing by reference
467 That convers the const-iterator-only situation. When we need separate
468 const and mutable iterators, one small complication is added beyond
469 the simple addition of a second class.
473 typedef something_or_other value_type;
474 class const_iterator;
476 public std::iterator<std::forward_iterator_tag, value_type> {
477 friend class container;
478 friend class container::const_iterator;
480 value_type& operator*() const;
481 value_type* operator->() const;
482 iterator& operator++();
483 iterator operator++(int);
484 friend bool operator==(iterator lhs, iterator rhs);
485 friend bool operator!=(iterator lhs, iterator rhs);
489 class const_iterator:
490 public std::iterator<std::forward_iterator_tag, value_type> {
491 friend class container;
494 const_iterator(const iterator& i);
495 const value_type& operator*() const;
496 const value_type* operator->() const;
497 const_iterator& operator++();
498 const_iterator operator++(int);
499 friend bool operator==(const_iterator lhs,
501 friend bool operator!=(const_iterator lhs,
509 There needs to be a conversion from iterator to const_iterator (so
510 that mixed-type operations, such as comparison between an iterator and
511 a const_iterator, will work). This is done here by giving
512 const_iterator a conversion constructor from iterator (equivalently,
513 we could have given iterator an operator const_iterator()), which
514 requires const_iterator to be a friend of iterator, so it can copy its
515 data members. (It also requires the addition of an explicit default
516 constructor to const_iterator, since the existence of another
517 user-defined constructor inhibits the compiler-defined one.)
519 Bidirectional iterators add just two member functions to forward
523 public std::iterator<std::bidirectional_iterator_tag, value_type> {
526 iterator& operator--();
527 iterator operator--(int);
531 I won't detail the implementations, they're obvious variations on
534 Random access iterators add several more member and friend functions:
537 public std::iterator<std::random_access_iterator_tag, value_type> {
540 iterator& operator+=(difference_type rhs);
541 iterator& operator-=(difference_type rhs);
542 friend iterator operator+(iterator lhs, difference_type rhs);
543 friend iterator operator+(difference_type lhs, iterator rhs);
544 friend iterator operator-(iterator lhs, difference_type rhs);
545 friend difference_type operator-(iterator lhs, iterator rhs);
546 friend bool operator<(iterator lhs, iterator rhs);
547 friend bool operator>(iterator lhs, iterator rhs);
548 friend bool operator<=(iterator lhs, iterator rhs);
549 friend bool operator>=(iterator lhs, iterator rhs);
554 container::iterator::operator+=(container::difference_type rhs) {
555 // add rhs to iterator position
560 container::iterator::operator-=(container::difference_type rhs) {
561 // subtract rhs from iterator position
565 container::iterator operator+(container::iterator lhs,
566 container::difference_type rhs) {
567 return iterator(lhs) += rhs;
570 container::iterator operator+(container::difference_type lhs,
571 container::iterator rhs) {
572 return iterator(rhs) += lhs;
575 container::iterator operator-(container::iterator lhs,
576 container::difference_type rhs) {
577 return iterator(lhs) -= rhs;
580 container::difference_type operator-(container::iterator lhs,
581 container::iterator rhs) {
582 // calculate distance between iterators
585 bool operator<(container::iterator lhs, container::iterator rhs) {
586 // perform less-than comparison
589 bool operator>(container::iterator lhs, container::iterator rhs) {
593 bool operator<=(container::iterator lhs, container::iterator rhs) {
597 bool operator>=(container::iterator lhs, container::iterator rhs) {
601 Four of the functions (operator+=(), operator-=(), the second
602 operator-(), and operator<()) are nontrivial; the rest are
605 One feature of the above code that some experts may disapprove of is
606 the declaration of all the free functions as friends, when in fact
607 only a few of them need direct access to the iterator's private data.
608 I originally got into the habit of doing this simply to keep the
609 declarations together; declaring some functions inside the class and
610 some outside seemed awkward. Since then, though, I've been told that
611 there's a subtle difference in the way name lookup works for functions
612 declared inside a class (as friends) and outside, so keeping them
613 together in the class is probably a good idea for practical as well as
616 I hope all this is some help to anyone who needs to write their own
617 STL-like containers and iterators.
620 Ross Smith <ross.s@ihug.co.nz> The Internet Group, Auckland, New Zealand
624 <!-- *********************************************************************** -->
625 </ul><table width="100%" bgcolor="#330077" border=0 cellpadding=4 cellspacing=0><tr><td align=center><font color="#EEEEFF" size=+2 face="Georgia,Palatino"><b>
626 <a name="seealso">See Also
627 </b></font></td></tr></table><ul>
628 <!-- *********************************************************************** -->
630 A lot of these comments and recommendations have been culled for other sources. Two particularly important books for our work are:<p>
633 <li><a href="http://www.aw.com/product/0,2627,0201924889,00.html">Effective C++</a> by Scott Meyers. There is an online version of the book (only some chapters though) <a href="http://www.awlonline.com/cseng/meyerscddemo/">available as well</a>.
634 <li><a href="http://cseng.aw.com/book/0,3828,0201633620,00.html">Large-Scale C++ Software Design</a> by John Lakos
637 If you get some free time, and you haven't read them: do so, you might learn something. :)
640 <!-- *********************************************************************** -->
642 <!-- *********************************************************************** -->
646 <address><a href="mailto:sabre@nondot.org">Chris Lattner</a></address>
647 <!-- Created: Tue Jan 23 15:19:28 CST 2001 -->
649 Last modified: Mon Oct 1 15:33:40 CDT 2001
projects / oota-llvm.git / blob